Group Assignment

We measured the power consumption of two output devices: three WS2812B NeoPixels and a stepper motor. Both were connected to a development board designed during the Electronic Production week.

Method

We used a digital multimeter in current measurement mode, placing the probes in the current input and placing the meter in series with the power supply. The bench power supply was set to 5V with a 0.5A current limit. The NeoPixels were programmed to display white light at 50/255 (~20%) brightness.

Results

Calculation Example

• NeoPixel Power: 0.0337 A × 5.0 V = 0.168 W
• Motor Power: 0.011 A × 5.0 V = 0.055 W
• Scaling example: Running 20 NeoPixels for 3 hours would require ~3.2 Wh (640 mAh at 5V).

You can access the group Assignment here.

Output Devices

Output devices receive processed data from a computer and translate it into visual, audio, or physical forms for the user.

Common types include monitors for display, printers for hard copies, and speakers for sound.

I wanted to add a motor to my final project. I was confused between a stepper motor and a servo motor. So I went and checked up on both of them. Here's what I learned:

Stepper motors move in fixed steps and never report back, so if you say 200 steps, they do 200 steps.

Servo motors have encoders, so the controller actually knows where the motor ended up and can correct if it drifted.

Steppers are cheaper and good at holding a position. Servos are better when the motion needs to be fast or the load varies, because you get real feedback about what actually happened.

I went ahead with the stepper motor.

Stepper Motor

A stepper motor, also referred to as a step motor or stepping motor, is a brushless DC electric motor that rotates in a series of small, discrete angular steps rather than spinning continuously like conventional DC motors.

Stepper motors find widespread use across diverse sectors, from consumer electronics such as printers and scanners to sophisticated industrial equipment including CNC machines, 3D printers, robotics, medical instruments, and precision optical systems.

Working Principle

The operation of a stepper motor is rooted in electromagnetic induction and the sequential energisation of stator windings.

Like all electric motors, a stepper motor consists of a stationary part (the stator) and a moving part (the rotor).

The stator contains multiple coils arranged in phases, while the rotor may be a permanent magnet, a toothed soft-iron structure, or a hybrid combination of both.

The fundamental operating sequence is as follows: when a current pulse is applied to a particular stator winding, it generates a magnetic field. The rotor aligns itself with this field due to magnetic attraction. When the next winding in the sequence is energised, the magnetic field shifts position, causing the rotor to advance by a fixed angular displacement—this displacement is known as the step angle. By continuously energising the windings in a specific order, the rotor rotates step by step. The step angle depends on the motor’s physical construction and determines how many steps are required for one complete revolution.

A typical stepper motor has a step angle of 1.8°, translating to 200 full steps per revolution. Mechanically, when the motor transitions from one step to the next, the rotor overshoots the target position and oscillates around it before settling—similar to a mass-spring system. The magnitude of this oscillation depends on the step size, load inertia, and damping characteristics.

Step Angle and Resolution

The step angle (θ) is the angular displacement of the rotor for each input pulse. It is determined by the motor’s construction and can be calculated using:
θ = 360° / (Nᵣ × Ø)
where Nᵣ is the total number of rotor teeth and Ø is the number of motor phases. Common step angles include 1.8° (200 steps/rev), 0.9° (400 steps/rev), and 7.5° (48 steps/rev).

Types of Stepper Motors

Stepper motors are classified into three primary types based on rotor construction: Permanent Magnet (PM), Variable Reluctance (VR), and Hybrid Synchronous. Each type offers distinct characteristics suited to different application requirements.

Stepper Motor Driver

A stepper motor driver is an electronic amplifier that translates low-current signals from a microcontroller into the high-current pulses needed to rotate a stepper motor. It manages coil energization, controls the motor's direction, and often enables advanced microstepping for smoother, quieter, and highly precise positioning.

The DRV8825. Though small in size, this chip is packed with powerful features. This driver can handle up to 45V and deliver 2.5A of electrical current, which is enough power to run popular stepper motors like the NEMA 17 and NEMA 23.

One of the best features of the DRV8825 is its built-in "translator." Normally, you would need to send complex electrical signals to four different wires in a specific order; the translator simplifies this to two pins: STEP (one pulse equals one step) and DIR (direction).

Technical Specifications

Power Pins

VMOT and GND pins supply power to both the driver and the stepper motor. This voltage can range from 8.2V to 45V.

Microstepping Pins

The DRV8825 offers six resolution options configured via the M0, M1, and M2 pins.

Note: These pins have internal pull-down resistors, so leaving them unconnected defaults the motor to Full-step mode.

Control Input Pins

• STEP: Each HIGH pulse moves the motor by one step. The pulse frequency determines the rotation speed.
• DIR: Controls rotation direction (HIGH for clockwise, LOW for counterclockwise).

Power State Control Pins

• EN (Enable): Active-low pin. Pulling it LOW enables the driver (default state).
• SLP (Sleep): Active-low pin. Pulling it LOW puts the driver into power-saving mode.
• RST (Reset): Active-low pin. Resets the driver and returns the motor to its starting position.

Note: Both SLP and RST must be HIGH to enable the driver. You can bridge them to a logic HIGH voltage or control them via microcontroller GPIO.

Fault Detection Pin

The FAULT output goes LOW whenever the driver detects an error condition like over-current or thermal shutdown. The driver remains disabled until RESET is toggled or VMOT power is cycled.

Output Pins

Connect your bipolar stepper motor coils here: A1/A2 for the first coil and B1/B2 for the second coil.

OLED

An Organic Light Emitting Diode (OLED) works by passing an electric current through organic material layers sandwiched between an anode and a cathode. When voltage is applied, the anode injects holes (positive charge) and the cathode injects electrons (negative charge) into these layers, which recombine in the emissive layer to create light through electroluminescence.

Advantages of OLEDs

• Self-Emissive: Unlike LCDs, OLED pixels create their own light, allowing for true blacks, higher contrast, and no need for a backlight.
• Thin & Flexible: Organic layers are thin, enabling flexible, foldable, and lightweight displays.
• High Response Times: They offer faster refresh rates, suitable for fast-paced content.

OLEDs are commonly used in smartphones, high-end TVs, and wearable devices.

I2C (4-Pin) Module

This is the most common version and requires only two data lines for communication. It is widely used due to its simplicity and low pin count.

• GND: Ground (0V).
• VCC: Power supply (typically 3.3V to 5V).
• SCL: Serial Clock line for I2C communication.
• SDA: Serial Data line for I2C communication.

SPI (7-Pin) Module

SPI is used for faster communication and offers more control pins. This interface is often preferred for applications requiring higher refresh rates or more complex graphics.

• GND: Ground (0V).
• VCC: Power supply (typically 3.3V to 5V).
• D0 (CLK): Serial Clock pin for SPI communication.
• D1 (MOSI): Serial Data pin for SPI communication.
• RES (RESET): Used to reset the display to its initial state.
• DC (Data/Command): Selects between sending data or commands to the controller.
• CS (Chip Select): Used to activate the display for communication.

BUZZER

The 9032 SMD Passive Buzzer is a compact electromagnetic sound component used for providing auditory feedback in miniature electronic devices. Unlike active buzzers, it requires an external oscillation circuit (PWM signal) to produce sound.

Usage Tips

• Drive Circuit: Use a MOSFET or Transistor to drive the buzzer from a microcontroller, as the 100mA current requirement may exceed the direct output capacity of standard GPIO pins.
• Tone Generation: By varying the frequency of the input PWM signal, you can generate different musical tones and vary the loudness of the alert.

Individual Assignment

So for my assignment or this week, I wanted to use a stepper motor and an led. And I decided to use Xiao DRV8825 as the stepper motor driver.

Designing a Custom Footprint for the DRV8825 Driver

The DRV8825 module has two rows of 8 pins. To ensure a perfect fit on my custom PCB, I designed a specialized footprint in KiCad by aligning two 1x08 female header sockets.

I updated the footprints in the PCB Editor and adjusted the grid to 2.54mm (0.1 inch) to match the standard breadboard pitch of the module.

I matched the Y-coordinates of both rows to ensure they were perfectly parallel, then calculated the horizontal offset.

By measuring the physical DRV8825 board, I confirmed the span between the two rows is exactly 12.7mm (0.5 inches).

I grouped the components to preserve this relative spacing during the rest of the board layout process.

Final Schematic Overview

I integrated the custom footprint into the final design, which includes the XIAO controller, the DRV8825 driver, feedback LEDs, and a buzzer.

Instead of typing the constraaints manually, I imported the settings from a previous board I made.

I used two different track width. I created them in the 'Pre-defined Sizes' tab.

.4 mm and .8 mm.

.8 mm was for power lines.

You can change the track widths in this tab.